# SURFL "elevation" and "azimuth" definition

2 views (last 30 days)
Fadhli Atarita on 26 Mar 2021
Commented: Fadhli Atarita on 9 Apr 2021
Hello,
I need to extract the reflectance data from the "surfl" function but I am having trouble in understanding the "azimuth" and "elevation" parameters of this function. The function uses a default value which is defined as "The default s is 45° counterclockwise from the current view direction". What is this "current view direction" because I don't set any "view" fuction for the plot?
However, after playing around with multiple figures and AZ and EL parameters, I think that the AZ=0 deg means in the south direction of the data and EL=0 is the horizon. What is the unit of the EL parameter? Is it in degrees? I've tried using EL=90 and it seemed like it was from nadir but I'm still not sure.
Please let me know if I got this right.
Thank you.

Chidvi Modala on 30 Mar 2021
You may refer to the below link for a clear understanding on viewpoints
Fadhli Atarita on 30 Mar 2021
Hi,
What I'm still confused of is that a 3D plot has a default viewpoint of azimuth = -37.5° and elevation = 30°. and in the documentation of surfl, it is stated that s= "Direction from the surface to the light source, specified as a two- or three-element vector. The vector has the form [sx sy sz] or [azimuth elevation]. The default direction is 45° counterclockwise from the current view direction."
Does that mean 45° from the -37.5° viewpoint (which is basically 7.5°) or literally 45° regardless of the default 3D viewpoint ? and there is no stated default elevation, can i assume that it is 0°?

Chidvi Modala on 5 Apr 2021
surfl doesn't have a default viewpoint, the view belongs to the axes. Consider:
view(3)
[az,el] = view
az =
-37.5000
el =
30
view([10,20])
[az,el] = view
az =
10
el =
20
If the s parameter is not specified it is calculated as 45 degrees counterclockwise from the current view direction.
The light is placed at the coordinate [Sx,Sy,Sz] where:
Sx = cos(az)*sin(45)+sin(az)*cos(el)*cos(45)
Sy = sin(45)*sin(az)-cos(az)*cos(el)*cos(45);
Sz = sin(45)*sin(el);
If the s parameter is specified as a two element vector: Saz, Sel, the light is placed at:
Sx = sin(Saz)*cos(Sel)
Sy = -cos(Saz)*cos(Sel)
Sz = sin(Sel)
If the s parameter is specified as a three element vector, we use those elements to define Sx, Sy, Sz.
If you'd like to learn more about where the light is placed, feel free to experiment with:
h=surfl(rand(5),rand(5),rand(5), [0 0], 'light');
h(2).Position
You can also experiment with:
edit surfl.m
Fadhli Atarita on 9 Apr 2021
Thank you!

R2020b

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!